An extended depth of field (EDOF) technique that can be used in reducing an optical blur and enlarging a in-focus range typically includes following two approaches.
A first approach is a technique using a single point spread function (PSF) which does not vary according to a depth. To be specific, an image is captured using an optical system configured to obtain the PSF which does not vary according to the depth. Then, the single PSF is used for performing restoration processing on a captured image. This is referred to as a depth invariant method, hereinafter.
As one of methods with highest efficiency in this approach, a method using an image which is captured with varying an in-focus position (focal sweep or flexible depth of field (F-DOF)) has been proposed (see non-patent literature (NPL) 1).
A second approach is a technique using a PSF which varies according to a depth. To be specific, in the technique, a depth of a captured scene (depth data) is detected and restoration processing is performed on a captured image using the PSF corresponding to the detected depth. This is referred to as a depth variant method, hereinafter.
As a representative method in this approach, a method is proposed which uses an image captured using a coded aperture or a lattice focal lens (see NPL 2 and NPL 3). Particularly, the lattice focal lens is known to extend a depth of field most efficiently, in the both approaches.
In addition, the depth variant method also has an advantage that the depth data which cannot be obtained by the depth invariant method can be also obtained at once.
With such an EDOF technique, an optical blur in an area which is out of focus in a captured image can be reduced, to thereby extend the depth of field of the captured image.